1. Field of the Invention
The present invention relates to an etch-resistant composition, and specifically, relates to an etch-resistant composition which is both acid-resistant and base-resistant. The etch-resistant composition can be applied in preparing a selective emitter of a solar cell.
2. Descriptions of the Related Art
Due to the increasingly serious environmental problems of energy shortages, greenhouse effect, etc., various countries are actively developing alternative energy sources, such as solar cells. FIG. 1 is a diagram of a typical solar cell, in which an n-type doping layer 2 is formed on a p-type silicon semiconductor substrate 1 through a doping process, and then an anti-reflective layer 3 (such as silicon nitride) and electrodes 4 are formed onto the n-type doping layer 2. Herein, the conductive types of the silicon semiconductor substrate 1 and the doping layer 2 can be interchanged. That is, the conductive types can also be a combination of an n-type silicon semiconductor substrate and a p-type doping layer.
It is well known that light absorbed by a solar cell is prone to be dissipated as heat or in forms of recombination of current carriers at high doping concentration, and thus, the photoelectric conversion efficiency is lowered. To reduce the above-mentioned cases, generally, doping layers with lower doping concentration and shallow depth are selected and used; however, these doping layers with lower doping concentration and shallow depth will face problems such as poor conduction. “Selective emitter” technique has been developed in the industry, which is characterized by forming a doping layer that is heavily doped underneath the electrode while forming a doping layer that is lightly doped in the light-affected area on which no electrode is set.
Among several methods for manufacturing a selective emitter, an etch back method attracts much attention. In brief, the etch back method is described as follows: forming an etch-resistant layer 7 (mask) as shown in FIG. 2 at a predetermined electrode region (or non light-affected area) in a printing manner, and then performing etching to remove part of the doping layer in the unmasked region (i.e., the predetermined light-affected area) to thereby make the unmasked region a lightly doped one and the predetermined electrode region remain heavily doped. In this manner, the light that is absorbed by the solar cell is dissipated less as heat and less in forms of recombination of current carriers without damaging conductivity, and thus, photoelectric conversion efficiency is elevated. Herein, the known etch-resistant materials for forming an etch-resistant layer are usually either acid-resistant or base-resistant, and therefore, are unable to be used under various etching conditions (such as base etching or acid etching). As a result, an etch-resistant material which is both acid-resistant and base-resistant and is applicable under various etching conditions is in high demand in the industry.
In this regard, the present invention provides an etch-resistant composition which possesses excellent printing property and is resistant to acid as well as base, and the etch-resistant layer formed thereby can be removed simply by an organic solvent or a heat treatment. Thus, the etch-resistant composition of the present invention can be used under various etching processes (such as manufacturing a selective emitter of a solar cell) and the convenience is greatly increased.